Antifouling polymers

ABSTRACT

A range of extruded polymers incorporating synthetic furanones was manufactured and field tested. Polymers incorporating furanones showed excellent antifouling efficacy and significantly reduced fouling for more than 100 days. 
     The present inventors have developed polymers that release commercial short-lived biocides or analogues of antifouling compounds isolated from marine algae. A range of polymers incorporating either the commercial isothiazolone Sea-Nine 211™ or a halogenated furanone were effective antifouling treatments in laboratory and field trials. The efficacy of the polymers was dependant on polymer type and the initial concentration of the antifouling compound. The polymers can be extruded as filaments that can be woven into netting or extruded or molding for other applications. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

TECHNICAL FIELD

The present invention is directed to polymer compositions havinganti-fouling activity, particularly polymer compositions suitable formarine and fresh water applications.

BACKGROUND ART

Biofouling presents a severe operational problem to aquaculture forexample. On fish cages, it restricts water flow through netting whichreduces the supply of dissolved oxygen and the removal of excess feedand waste products. In suspended shell-fish culture, a large mass offouling can compete with the cultured species for food and space, andcan overwhelm flotation capacity. Current metal-based antifoulants areundesirable for aquaculture because of possible adverse environmentaleffects, and consumer concerns that may jeopardise market image.Commercially available, but biodegradable compounds, or naturallyoccurring antifoulants extracted from marine organisms, may provide anacceptable solution by offering broad spectrum activity, and in the caseof natural antifoulants, acting via chemical deterrence rather thantoxicity.

Commercialisation of antifouling technology other than paints is stillin its infancy, and few field trials are reported in the literature.Although there are many antifouling agents and compositions presentlyavailable, the methods typically used to protect an object from foulingin an aqueous environment involve applying some form of protectivecoating to the surface of the object. Unfortunately, this approach isnot suitable for all applications and there is a need for other means ofprotecting such objects from microbial- or macro-fouling. The presentinventors have developed new polymer compositions that containantifouling agents which have surprising broad-spectrum antifoulingcharacteristics over prolonged periods and at lower concentrations thanwere previously believed possible.

DISCLOSURE OF INVENTION

In a first general aspect, the present invention consists in a polymercomposition having antifouling activity, the composition including apolymer and an organic antifouling agent, and having broad-spectrumantifouling activity for a prolonged period of at least 100 days whensubstantially immersed in a natural aqueous environment.

The polymer may be any polymer suitable for preparation by extrusionprocesses known to the art. In particular, polymers containingethylene-vinyl acetate copolymer (EVA), high-density polyethylene(HDPE), nylon, polypropylene (PP), sodium ionomer, copolymer of ethyleneand acrylic acid, or mixtures thereof are suitable. The presentinvention has been particularly successful using EVA, HDPE polymers, ormixtures thereof. It will be appreciated, however, that other polymersor mixtures may also be suitable to produce antifouling polymercompositions with prolonged and broad-spectrum antifouling activityaccording to the present invention.

The antifouling agents suitable for the present invention are syntheticantifouling agents belonging to the families of isothiazolones,furanones, or combinations thereof. Examples of suitable isothiazolonesand furanones are shown in FIG. 1. Preferably, the isothiazoloneantifouling agent is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-oneproduced and sold by Rohm and Haas under the name Sea-Nine 211™.

Preferably, the furanone antifouling agent is a mixture of thehalogenated furanones referred herein as 26/27 or 33/34 where

26 is(1′RS,5E)-3-(1′-Bromoethyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone;

27 is (1′RS)-3-(1′-Bromoethyl)-5-(dibromomethylidene)-2(5H)-furanone;

33 is(1′RS,5Z)-3-(1′-Bromohexyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone;and

34 is (1′RS)-3-(1′-Bromohexyl)-5-(dibromomethylidene)-2(5H)-furanone.

In a preferred embodiment of the first aspect of the present invention,the antifouling agents are used at a concentration of about 0.1 to 20%,more preferably from about 1 to 10% (w/w) of polymer composition. Itwill be appreciated that mixtures of antifouling agents (natural,synthetic, or commercial) may also be used to prepare the polymercompositions according to the present invention.

When using the antifouling agents in the form of isothiazolones orfuranones, the present inventors have made the surprising discovery thatin use the polymer compositions release amounts of the agent that wouldnot be expected to prevent fouling by organisms. Release studies foundthat the activity was caused by about ten-fold less of the agent thanwhat has been shown previously. The compositions that had good andpersistent activity over a prolonged period released less than 5, and inseveral cases less than 1 μg/cm²/day of the agent. Preferably, theserelease rates are obtained.

The polymer compositions according to the present invention hadsignificant antifouling activity when tested in marine environments.Preferably the antifouling activity lasts for at least 100 days, morepreferably at least 200 days, and even more preferably at least 300days.

It will be appreciated that the use of the term natural aqueousenvironment is meant to include oceans, estuaries, lakes, ponds, riversand aqueous environments where microorganisms (bacteria) ormacroorganisms (algae, plants, invertebrates or other taxa) are known tocause fouling, or there is the potential for such fouling.

The polymer compositions according to the present invention can be madeby any known means but preferably made by extrusion or moldingprocesses. The distinct advantage of this form of manufacture is thatthere is the possibility of controlling or manipulating the type ofcomposition produced. For example, fibers may be produced that can bewoven into nets, ropes and the like for use in the aquaculture industry.Also, solid structures can be extruded or molded in the form of cages,crates or structural materials for use in aqueous environments.Moreover, the extrusion or molding processes result in efficientblending of the polymer and active ingredient, a factor influencing thelow release rates observed by the present inventors.

It will be appreciated that the present invention is not restricted touse in aquaculture applications. Any situation in aqueous conditionswhere there is a problem of fouling may be applicable. For example,pipes and plumbing equipment may be made from the polymers according tothe present invention.

In a preferred form, the present invention consists in a polymercomposition having broad-spectrum antifouling activity comprising apolymer selected from the group consisting of ethylene-vinyl acetatecopolymer (EVA), high-density polyethylene (HDPE), sodium ionomer,copolymer of ethylene and acrylic acid, and mixtures thereof and one ormore organic antifouling agents selected from the group consisting ofantifouling agents belonging to the families of isothiazolones,furanones, and combinations thereof, wherein in use the polymer hasbroad-spectrum antifouling activity for a prolonged period of at least100 days, preferably at least 200 days, more preferably at least 250days, and most preferably for at least 300 days when the composition issubstantially immersed in a natural aqueous environment, preferably amarine environment.

In a further preferred form, the present invention consists in anantifouling polymer composition comprising a polymer and anisothiazolone or one or more furanone antifouling agents or mixturesthereof, the composition capable of maintaining broad-spectrumantifouling activity in an natural aqueous environment, preferably amarine environment, by releasing less than about 3-5 μg/cm²/day of theantifouling agent over a period of greater than 100 days, preferablyover 200 days.

The initial release rates of the antifouling agents from the polymers inthe first few days of exposure to an aqueous environment were muchhigher than the values listed above. What was surprising was the findingthat after this initial high release rate, there was sustainedantifouling activity (greater than 100 days) of the polymers accordingto the present invention caused by release of very low levels ofantifouling agents.

In a second aspect, the present invention consists in the use of theantifouling compositions according to the first aspect of the presentinvention in the preparation of extruded or molded articles havingsustained broad-spectrum antifouling activity for at least 100 days whensubstantially immersed in a natural aqueous environment.

In a third aspect, the present invention consists in the use of anisothiazolone or one or more furanone antifouling agents, in themanufacture of an antifouling polymer composition having broad spectrumantifouling activity for at least 100 days when the polymer issubstantially immersed in a natural aqueous environment.

In a fourth aspect, the present invention consists in an article madefrom a composition according to the first aspect of the presentinvention, the article having broad spectrum antifouling activity for atleast 100 days when substantially immersed in a natural aqueousenvironment.

Throughout this specification, unless the context requires otherwise,the word “comprise”, or variations such as “comprises” or “comprising”,will be understood to imply the inclusion of a stated element, integeror step, or group of elements, integers or steps, but not the exclusionof any other element, integer or step, or group of elements, integers orsteps.

In order that the present invention may be more clearly understood,preferred forms will be described with reference to the followingexamples and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows examples of suitable isothiazolones and furanones for thepresent invention. In FIG. 1B (isothiazolones), R₁, R₂ and R₃ are eithera hydrogen atom, methyl, alkyl, hydroxyl, ether, halogen, sulfur,nitrogen or a combination thereof. In FIG. 1C (furanones), R₁, R₂, andR₃ are either a hydrogen atom, a hydroxyl group, an alkyl group, anester group, or a halogenated alkene; or R₁ and R₂ together are anunsubstituted or a halogenated alkene, R₄ is a hydrogen or a halogenatom, and R₅ is a hydrogen or an alkyl group.

FIG. 2 shows the growth of the marine bacterium Vibrio fischeri inculture with polymers incorporating commercial biocides and algalextracts (Data are means±SE, N=3).

FIG. 3 shows the settlement success of cyprid larvae of Balanusamphitrite on polymers incorporating commercial biocides and algalextracts (Data are means±SE, N=3).

FIG. 4 shows the settlement of larvae of Bulgla neritina on polymersincorporating commercial biocides and algal extracts (Data are means±SE,N=3).

FIG. 5 shows quantities of Sea-Nine 211™ remaining in Dupont Elvax 470during field exposure. Each point is the mean of 4 samples,bars=standard error.

FIG. 6 shows quantities of the halogenated furanone remaining in DupontElvax 470 during field exposure. Each point is the mean of 4 samples,bars=standard error.

FIG. 7 shows release rate of Sea-Nine 211™ from Dupont Elvax 470 (EVA).

FIG. 8 shows leaching rates for Sea-Nine 211™ from EVA polymers.

FIG. 9 shows leaching rates for Sea-Nine 211™ from HDPE and EVA blendedpolymers.

FIG. 10 shows leaching rates for Sea-Nine 211™ from nylon and EVAblended polymers.

MODES FOR CARRYING OUT THE INVENTION

The present inventors have carried out laboratory and field trials ofextruded polymers (plastics) that incorporate antifouling compounds.These polymers can be extruded as filaments for fish-cage netting and asrigid mesh for shell-fish containment. Antifouling efficacy wasevaluated for polymers incorporating either an algal extract, an analogof a compound that occurs in one of these extracts, or one of fourcommercially-available organic biocides. Antifoulant release fromdifferent types of polymer and from polymers with different antifoulantloadings was also investigated. Analysis of micro- and macro-foulingsuccession clearly demonstrates the potential for polymer-based deliveryof antifoulants, and has identified future directions for research intoenvironmentally-acceptable aquaculture antifouling.

MATERIALS AND METHODS

To incorporate commercial biocides, algal extracts or natural productanalogues into polymers, the active ingredients were coated onto thepolymer beads and compounded as follows:

EXAMPLE I Single Polymer (HDPE) Incorporating Sea-Nine 211™

The materials were prepared by extruding narrow sheets using a HaakeRheocode 90 system equipped with a laboratory-scale Rheomex TW 100counter-rotation twin screw extruder fitted with a slit die. Thedimensions of the die were: width=15 cm and thickness=1 mm. The Sea-Nine211™ was premixed with HDPE in the formulation: HDPE: Dried Sea-Nine211™=95:5.

The screw rotation speed was 50 rpm. The temperature profile along theextruder barrel was set at 160, 170, 180, 170° C. (from feed zone todie).

EXAMPLE II Polymer Blends (HDPE/EVA) Incorporating Sea-Nine 211™

Step 1:

Sea-Nine 211™ is incorporated into EVA at a loading of 10% using a HaakeRheocord 90 system equipped with a laboratory-scale Rheomex TW 100counter-rotating twin screw extruder fitted with a rod die (F 2 mm). TheSea-Nine 211™ was premixed with EVA in the formulation: EVA:Sea-Nine211™=90:10.

The screw speed was 60 rpm. The temperature profile along the extruderbarrel was set at 110, 110, 120, 130° C. (from feed zone to die). Theextruded materials were granulated for next application.

Step II:

HDPE was blended with the EVA incorporating with Sea-Nine 211™ using aHaake Rheocord 90 system equipped with a laboratory-scale Rheomex TW 100counter-rotating twin screw extruder fitted with a slit die. Thedimensions of the die were: width=15 cm and thickness=1 mm. The EVAincorporating with Sea-Nine 211™ was premixed with HDPE in theformulation: HDPE:EVA incorporating Sea-Nine 211™=90:10. The finalSea-Nine 211™ concentration in polymers is 1%. The screw rotation speedwas 50 rpm. The temperature profile along the extruder barrel was set at160, 170, 180, 170° C. (from feed zone to die).

To minimise the exposure of active ingredients to the harsh conditionsof processing, the polymer strips were manufactured in a single step,i.e. pellets of polymer and active compounds were fed into the extruder,compounded and formed into a sheet in one step. Polymers were extrudedas strips 400 μm thick by 10 cm wide.

Preparation of algal extracts and metabolites

For the algal extracts, the two species of algae were collected in NewSouth Wales, Australia. The algal tissue was frozen, freeze dried,extracted with dichloromethane and the resulting crude extract reducedin vacuo. Furanones were extracted and purified as per de Nys et al(1993, 1995).

Place of field trials

All field trials were conducted at Huon Aquaculture Company's lease atHideaway Bay (43° 20′ S, 147° 01′ E), in the Huon River, Tasmania,Australia. The site is fully marine, except for a 2-5% salinity drop to1 m depth after high rainfall in winter. Water temperatures range from11° to 17°. Water movement is dominated by tidal flow and current speedvaries from 5 to 20 cm/s.

Polymer-based delivery of antifouling compounds I

Antifouling polymers were produced from one polymer type (Dupont Elvax®3165SB, ethylene-vinyl acetate) which incorporated either a commercialbiocide (Busan 11-M1™, Irgarol 1051™(2-methyl-4-tert-butylamino-6-cyclopropylamino-s-triazine; Ciba-Geigy),Nopcocide N-96™ (tetrachloroisophthalonitrile; Henkel), or Sea-Nine 211™(4,5-dichloro-2-n-octyl-4-isothiazolin-3-one; Rohm & Haas), or a crudealgal-extract (Delisea pulchra or Laurencia rigida). All biocides weretested as pure solids without solvent additives. Each antifoulant wasincorporated into the polymer at a nominal loading of 1% (of polymer dryweight), except for the D. pulchra extract which was included at nominalloadings of 1% and 5%. Subsequent GC-MS analyses revealed that loadingswere much lower than this (e.g., roughly 0.1% or less) in this trial.

Laboratory Bioassays

Polymer strips were tested in laboratory bioassays (according to de Nyset al., 1996) to determine inhibition of bacterial growth (Vibriofischeri, Serratia sp.), and settlement inhibition of barnacle cypridlarvae (Balanus amphitrite), bryozoan larvae (Bugula neritina), andsettlement and germination of spores of Ulva lactuca. Inhibition wascompared between treatment dishes (polymer with biocides or extractsincorporated), blank polymer controls (polymer without biocides orextracts incorporated), and untreated dishes (no polymer added). Thetreatment and polymer control dishes were prepared by fixing a disk ofpolymer (10 cm² area) to the base of a petri dish (9 cm² area). Alltreatments and controls were tested in triplicate. Polymers which wereineffective after the initial test (week 0) were discarded. Treatmentswhich were effective, because they either inhibited bacterial growth orlarval settlement, were placed in seawater (static) and re-tested atweekly intervals until their activity was not significantly differentfrom the blank polymer control. A new blank polymer control was includedin each weekly assay.

Field Trial

Polymer samples were cut into 25 cm strips for field testing, attachedrandomly within 2 large frames and immersed at 1 m depth. Extrudedpolymer without antifoulant was used as a control. A total of 59 stripswere used, but replication varied between treatments (depending onantifoulant availability). The trial commenced on Sep. 17, 1996, andfouling development was recorded using close-up and wide-angleunderwater photography after 25, 25, 60 and 75 days immersion.

To provide samples for scanning electron microscopy (SEM) smaller strips(3×13 cm) were attached to a third frame and fixed underneath one of thelarger strip-containing panels. Two strips were removed per treatmentafter 25, 35 and 75 days immersion. During sampling, a central 1 cm by 8cm block was excised from each strip and prepared for scanning electronmicroscopy (Hodson and Burke 1994). Each block was cut into eight 1 cmby 1 cm sections for observation.

Polymer-based delivery of antifouling compounds II

Eight types of polymer (Table 1) were combined with either Sea-Nine 211™or a combination of synthetic analogs (2/8/1) of a halogenated furanoneisolated from D. pulchra (2 is(5Z)-3-butyl-4-bromo-5-(bromomethylidene)-2(5H)-furanone; 8 is3-butyl-5-(dibromomethylidene)-2(5H)-furanone; and 1 is3-butyl-4-bromo-5-(dibromomethylidene)-2(5H)-furanone). The polymerswere chosen to give a range of release rates. A polymer equivalent tothat used in trial 1 (Dupont Elvax® 470) was used, but with antifoulantsat 1%, 5% and 10% loading. Twenty-five treatments were used in total: 8controls (each polymer without antifoulant), 10 combinations of Sea-Nine211™ and 7 combinations of the furanone (Table 2).

TABLE 1 Polymer types evaluated in trial II. Manufacturer Name ChemicalComposition Dupont Elvax ® 470^(a) Ethylene-vinyl acetate co- polymer(EVA)^(b) Elf atochem Evatane ® 1005 VN5 Ethylene-vinyl acetate co-polymer (EVA)^(b) Elf atochem Evatane ® 1020 VN3 Ethylene-vinyl acetateco- polymer (EVA)^(c) Elf atochem Evatane ® 28.03 Ethylene-vinyl acetateco- polymer (EVA)^(d) Kemcor HD 6095 High-density polyethylene (HDPE)Shell HET 6100 Polypropylene (PP) Dupont Surlyn ® 1707 Na⁺ ionomer BASFLucalen ® A Copolymer of ethylene and acrylic acid ^(a)equivalent toElvax ™ 3165 SB, used in trial I ^(b)8% vinyl acetate ^(c)18% vinylacetate ^(d)28% vinyl acetate

TABLE 2 Polymer and antifoulant combinations evaluated in trial II. Tenreplicates were used for each treatment, except where the number ofreplicates is specified in brackets. Percent Sea-Nine HalogenatedPolymer type antifoulant 211 ™ furanones^(a) Dupont Elvax ® 470 1% ✓ ✓Dupont Elvax ® 470 5% ✓     ✓(9) Dupont Elvax ® 470 10% ✓ ✓ Elf altochemEvatane ® 1005 VN5 1%   ✓ (6)  X^(b) Elf altochem Evatane ® 1020 VN3 1%  ✓ (7) X Elf altochem Evatane ® 28.03 1% ✓ X Kemcor HD 6095 1% ✓ ✓Shell HET 6100 1% ✓   ✓ (5) Dupont Surlyn ® 1707 1% ✓ ✓ BASF Lucalen ® A1% ✓ ✓ ^(a)The halogenated furanones were not included in all polymersbecause of limited quantity ^(b)X = combination not tested

Polymers were cut into 18.5 cm-long strips and attached to sections of10 cm-long PVC piping. The piping was used to create cylindrical testpanels (mounted vertically) as this shape has been found to reduceinconsistencies in fouling distribution, increase rapid colonisation bylocal fouling species and reduce orientation effects. The panels (n=248)were attached to 6 rows of a 6.0 by 9.0 m polyethylene raft. Rows 1 and2 were used for release-rate measurement, rows 3, 4 and 5 forphotographic records of fouling development, and row 6 (10 panels only)for SEM samples. The experiment was set up as a 1-way block design inrows 1 to 5, with randomised placement of duplicates for each treatmentin each row. Not all treatments were fully replicated, however, becauseof limited quantity of some polymers and of the natural product analog.

The raft was immersed at 1.5 m depth. After 20 days immersion 1 cm by 3cm samples were cut from each polymer-antifoulant panel in rows 1 and 2,and close-up underwater photographs were taken of all panels in rows 3,4 and 5. Sampling was repeated at approximately 3 week intervals untilall polymers failed to inhibit fouling. Because of severe fouling onmost panels, wide-angle photography was used after 125 days. Sampling ofrows 1 and 2 was reduced after 47 days because most treatments failed toinhibit fouling. Samples cut from rows 1 and 2 were used to quantify thelevel of antifoulant remaining (via gas chromatography-massspectrometry), and this data used for calculation of release rates.

RESULTS

Polymer-based delivery of antifouling compounds I

Laboratory Bioassays

Polymers incorporating commercial biocides and extracts significantlyinhibited the growth of the marine bacteria V. fischeri and Serratia sp.(FIG. 2; P<0.05, one-factor ANOVA followed by Tukey's test measured foreach assay). Different biocides and extracts had significantly differenteffects on the growth of both bacteria. The response of both species ofbacteria, however, was very similar for most compounds. Sea-Nine 211™was the most active compound, completely inhibiting the growth of bothV. fischeri and Serratia sp. for 3 weeks. D. pulchra extract (5%) wasthe next most active compound inhibiting the growth of both species fora period of 2 weeks. Of the other commercial products, Irgarol 1051™inhibited the growth of Serratia sp. for 2 weeks but was not effectiveagainst V. fischeri. Similarly Nopcocide N-96™ had differential effects,inhibiting the growth of V. fischeri up to 2 weeks, but only inhibitinggrowth of Serratia sp. for 1 week. The 1% loadings of each algal extracthad limited effect on bacterial growth and lost activity after 1 week.Busan 11-M1™ was the least effective compound and was not significantlydifferent from the blank polymer control.

The settlement of B. amphitrite cyprid larvae was significantlyinhibited by the polymers (FIG. 3: P<0.05, one-factor ANOVA followed byTukey's test). Sea-Nine 211™ and Nopcocide N-96™ were the most activecompounds completely inhibiting settlement for 17 weeks. The next mosteffective compound was L. rigida extract which after 17 weeks deterredsettlement by 80% compared to the control. D. pulchra extract (5%) wassignificantly less effective but remained significantly deterrent,inhibiting settlement by 40% compared to the control. The remainingtreatments, Irgarol 1051™ and 1% D. pulchra extract, lost activity after2 weeks. Busan 11-M1™ was the least effective compound and was notsignificantly different from the blank polymer control.

The biocides and extracts had significantly different effects on thesettlement of Bugula neritina larvae (FIG. 4; P<0.05, one-factor ANOVAfollowed by Tukey's test at each time tested). Sea-Nine 211™ was themost effective inhibitory compound, completely inhibiting settlement for6 weeks and remaining active up to 12 weeks. The next most activecompound was Nopcocide N-96™ which significantly deterred settlement forup to 12 weeks. The next group of active compounds, the algal extracts,had a much shorter period of efficacy of 2 weeks. Busan 11-M1™ andIrgarol 1051™ had no significant effect on the settlement of bryozoanlarvae.

Field trial

The antifouling effectiveness of both the commercial biocides and algalextracts was demonstrated after 25 days immersion. Polymers withbiocides Irgarol 1051™, Nopcocide N-96™ and Sea-Nine 211™ were unfouledand polymer with 5% D. pulchra extract had limited fouling. However, thecontrol polymer, polymers containing Busan 1-M1™, 1% D. pulchra extractor 1% L. rigida extract were heavily fouled. Furthermore, the polymerwith L. rigida extract had far greater fouling than the control polymer.The dominant fouling at this time was a tube-dwelling diatom (Naviculasp.), a common organism on salmon cages at this time of year. Of thefour effective antifouling treatments, Irgarol 1051™ and Sea-Nine 211™proved superior and still performed well after 60 days immersion. Thepolymer with 5% D. pulchra extract was fouled after 35 days, and thepolymer with Nopcocide N-96™ after 60 days.

Polymer observation with SEM clearly demonstrated the same relativeperformance of the four most effective treatments, but gave an earlierindication of their failure. Polymer with Sea-Nine 211™ performed best,and was only fouled by small colonies of bacteria after 25 daysimmersion. In comparison, the other two effective biocides displayed agreater level and diversity of macrofouling after 25 days. Polymercontaining 5% D. pulchra extract was extensively colonised by diatomswithin a thick mucilaginous layer. After 35 days polymer with Sea-Nine211™ was extensively colonised by diatoms, protista and bacteria, butfouling was less severe than on Irgarol 1051™ and Nopcocide N-96™. After60 days microorganisms were abundant on polymers with Irgarol 1051™ andSea-Nine 211™.

Polymer-based delivery of antifouling compounds II

Polymers incorporating either the halogenated furanone or Sea-Nine 211™effectively preventing fouling, although antifouling performance variedbetween treatments. Within 20 days of immersion all control polymerswere covered in tufts of diatoms, whereas all antifouling polymers hadeither no fouling or a thin diatom film (Table 3). Polymers containingthe furanone had good antifouling activity for 50 days, and the nominal5% and 10% loadings performed better than all other treatments. Six ofthe polymer types that incorporated Sea-Nine 211™ prevented macrofoulingfor 260 days immersion. These polymers were frequently fouling by diatomfilms, but these were poorly adhered and frequently sloughed from thepanels. The 5% and 10% loadings of Sea-Nine 211™ had the greatestantifouling effect, and completely prevented the formation of a diatomfilm for the first 180 days of immersion.

Analysis of the quantity of antifoulant remaining in each polymer duringthe trial demonstrated varying release rates for eachpolymer-antifoulant combination. A common trend for all polymer typesand concentrations was a high initial release rate during the first 20days, and then a gradual decline in release (FIGS. 5 and 6). Elvax3165SB® maintained a relatively constant release rate for Sea-Nine 211™after 100 days, and demonstrated that only small concentrations of thiscompound were required for effective antifouling (FIG. 7, Table 4).

Table 4 gives release rates for Sea-Nine 211™ from Elvax 3165SB (=Elvax470) over 250 days in the second field trial. Release rates were high,but soon decreased to <1 (1% loading) or ˜<5 (5% loading) μg/cm²/day. Inparticular both loadings had release rates much lower than 1 μg/cm²/dayafter 160 days in the field trial, but still effectively repelledmacrofouling.

TABLE 3 Field performance of antifouling polymers which were immersedfor 303 days Days immersion 20 34 47 61 90 110 125 146 160 181 209 259303 Control polymers Diatom tufts Macroalgae Sea-Nine 211 ™ Elvax 470(1%) — Diatom film Macroalgae Elvax 470 (5%) — — — — — — — — — — Diatomfilm Macroalgae Elvax 470 (10%) — — — — — — — — — — Diatom filmMacroalgae Evatane 1005 — Diatom film Macroalgae Evatane 1020 — Diatomfilm Macroalgae Evatane 28.03 — Diatom film Macroalgae Kemcor HD6095 —Diatom film Macroalgae Shell HET6100 D.film Diatom tufts MacroalgaeSurlyn 1707 D.film Diatom tufts Macroalgae Lucalen A — Diatom filmMacroalgae Halogenated furanones Elvax 470 (1%) D.film D.tuftsMacroalgae Elvax 470 (5%) — D.film D.tufts Macroalgae Elvax 470 (10%) —D.film D.tufts Macroalgae Kemcor HD6095 Diatom tufts Macroalgae ShellHET6100 Diatom tufts Macroalgae Surlyn 1707 Diatom tufts MacroalgaeLucalen A D.film Diatom tufts Macroalgae — No obvious fouling

TABLE 4 Release rates of Sea-Nine 211 ™ From Elvax 470 ™ in the field.1% and 5% loading. Release Rates (μg/cm²/day) Measurement period 1% 5%0-20 days 4.1 108.4 20-47 0.9 10.8 47-60 0.8 3.3 60-125 0.7 5.9 125-1600.2 3.4 160-209 0.3 0.16 209-250 0.01 0.11

A range of extrude polymers and antifouling compounds were combined toproduce materials with broad-spectrum antifouling efficacy (Table 1 and2). Seven types of antifouling compound were tested: two algal extracts(from Delisea pulchra and Laurencia rigida), a halogenated furanone, andfour commercial biocides (Busan 11-M1™, Irgarol 1051™, Nopcocide N-96™and Sea-Nine 211™). Several polymer-compound combinations were highlyefficient against fouling in both laboratory and field trials, and aresuitable for a range of commercial applications. These include theconstruction of materials for the aquaculture industry (eg. fish-cagenetting, mooring ropes, shellfish trays, rigid mesh panels, buoys andthe sides of aquaria) and other applications including piping andcooling-system intake screens.

Polymers incorporating the commercial isothiazolone Sea-Nine 211™ werehighly effective as antifouling materials (Table 3). Sea-Nine 211™ haspreviously been shown to affect a broad range of fouling taxa, and wasmore effective than Irgarol 1051™ and Nopcocide N-96™ against growth ofVibrio fischeri, settlement of the bryozoan B. neritina, and settlementand germination of spores of the alga Ulva lactuca (de Nys et al.,1996). Polymers that incorporate this compound are likely to havereduced environmental impact compared with traditional antifouling (eg.tributyl tin coatings), as Sea-Nine 211™ is claimed to rapidlybiodegrade (<24 hours) and to not bioaccumulate (Rohm & Haas materialssafety data sheets).

Polymers incorporating Sea-Nine 211™ were effective at release rates farlower than recommended for this biocide. The minimum effective releaserate (MERR) for Sea-Nine 211™10 μg/cm²/day (Takahashi and Mabuchi,1997). Vasishtha et al. (1995) recommended a MERR of 5-7 μg/cm²/day toprevent fouling by most taxa, with the exception of diatoms (15mg/cm²/day). In the present study (field trial 2) polymers effectivelyprevented macrofouling development at release rates lower (in the bestcase much lower—Table 4) than 1 μg/cm²/day (FIG. 7). At this releaserate the polymers did not prevent settlement of a diatom film. However,the release rates (even across a diatom film) were still sufficient toprevent macrofouling.

Such low release rates are ideal for aquaculture, because diatom foulingis not a concern, and the presence of diatoms suggests that releaserates were not excessive, ensuring the greatest antifouling lifetime. Itis noteworthy that those polymers that prevented development of a diatomfilm for up to 180 days (Table 3, 5% and 10% loadings of Sea-Nine 211™)were effective at release rates less than 200 nanograms/cm²/day (Tables3, 4). For aquaculture applications of course, the lower the releaserate the better (as long as fouling is still deterred) since impact onthe farmed species must be minimized.

The present study demonstrates that the release rate of Sea-Nine 211™can be controlled by polymer type (Table 1) and by manipulating theinitial compound concentration (FIG. 5: Table 4). The migration of anantifouling compound from within a polymer to the water interface isdependent on the diffusivity of the compound within the polymer. Theresistance to diffusion will depend on the similarity of the compoundand polymer (eg. their hydrophobicity and pH) and interactions betweenany functional groups of the compound and polymer. However, theantifouling performance of all polymers in the present study is notexplained by their relative release rate. The Shell PP™ had the greatestinitial concentration of Sea-Nine 211™, and a similar release rate toElvax 3165™ and Lucalen™, but had poor antifouling efficacy (Table 3).It is probable that this indicates a greater rate of compounddissolution from the polymer into seawater, and therefore a lowerconcentration at the surface. The present inventors also note thatinteractions between the polymer, and the active ingredient when itreaches the surface of the polymer, may be very important.

Control of release rates using Polymer Blends

From earlier work with Sea-Nine 211™ incorporated into the polymer EVA,it was shown that EVA performed the best in the field trials. However,attempts to significantly extend its active life by incorporating moreSea-Nine 211™ were unsuccessful. This was expected and was due to thezero and first order effects of a matrix device. Adding more activeingredients merely increases the early release rates so that excessivedumping of the component consumes the extra compound added. This can beseen in FIG. 8 where increasing the initial concentration from 4.5 to 6to 12 mg/g Sea-Nine 211™ resulted in very little improvement in theabsolute concentration at week 6, that is 0.2, 0.7. 1 mg/g remaining,respectively. It was discovered that by blending HDPE into the EVA theSea-Nine 211™ could be retained in the polymer during the initialrelease period. This is shown in FIG. 9 where with 90% HDPE blended intothe EVA (from an initial 11 mg/g loading). 6 mg/g remained in thepolymer after 6 weeks compared with 1 mg/g with no HDPE. With reducedamounts of HDPE, the retention effect was reduced. For example, the 70%HDPE only had 3 mg/g (from initial of 15 mg/g) after 6 weeks. The sameeffect was shown with nylon in FIG. 10 where 90% nylon has 5 mg/gremaining after 6 weeks from an initial 7 mg/g, and 70% nylon had 12mg/g remaining after 6 weeks from an initial 23 mg/g.

It has been found that the use of other polymers such as HDPE, nylon andthe like blended into EVA is an effective way to control the high earlyrelease rates of Sea-Nine 211™ when the loading of Sea-Nine 211™ isincreased.

Polymers incorporating halogenated furanones were also effective inlaboratory and field trials (FIGS. 1, 2, 3, 4: Table 3). Halogenatedfuranones are active against fouling algae, invertebrates and bacteria(de Nys et al., 1995). Furanones are highly active at low concentrations(10 ng-10 μg/ml) and effectively inhibit settlement without toxicity.The effective concentrations for furanones are an order of magnitudelower than copper and comparable to, or better than, effectiveconcentrations of Nopcocide N-96™, Irgarol 1051™ and Sea-Nine 211™ inlaboratory bioassays.

The difference in antifouling efficacy between Sea-Nine 211™ andfuranones appears to be due to the very low initial actual (as opposedto nominal) loadings of furanones, and the apparent need for a greaterMERR for these compounds in at least some of the polymers. With regardsto loading, the actual loadings of furanones in polymers in the secondfield trial were much less (between 0.1 and 0.35%) than the targetloading of 1%, and thus were much less than the loadings of Sea-Nine211™ in these trials. With regards to the need of a greater MERR,release rates of furanones from different polymers are shown in Table 5.Elvax 470 and Lucalen A were the most effective in inhibiting fouling,and release rates in these polymers during days 0-20 were ≧5 μg/cm²/day.Lucalen A, and Elvax 470 with 1% loading began to fail after ˜35 days,after leaching rates had dropped below 5 μg/cm²/day for 2 weeks (days20-35). Elvax 470 with a 5% loading of furanones maintained a leachingrate of ˜5 μg/cm²/day or higher through 35 days, and inhibiting foulingfor this period.

While leaching rates of these furanones thus need to be somewhat higherthan for Sea-Nine 211™, the present inventors noted that MERR of 5μg/cm²/day are very acceptable in both a commercial and environmentalsense. They are lower than the recommended MERR for Sea-Nine 211™(above).

TABLE 5 Release rates of furanones polymers in the field over 35 daysRelease Rates (μg/cm²/day) Polymers 0-20 days 20-35 Elvax 470 (5%) 38.04.7 Elvax 470 (1%) 5.0 1.4 Lucalen A 5.8 0.4 Kemcor 1.8 0 Shell 3.0 0Surlyn 0.1 0

Incorporation of synthetic furanones into extruded polymers—Antifoulingfield trial

MATERIALS AND METHODS

Nine polymers were extruded for field testing of antifouling efficacy(Table 6). To reduce the high release rates observed withnaturally-occurring furanones extracted from Delisea pulchra (previouspolymer trial) a combination of two synthetic furanone analogs wereused: 26/27 and 33/34 where 26 is(1′RS,5E)-3-(1′-Bromoethyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone;27 is (1′RS)-3-(1′-Bromoethyl)-5-(dibromomethylidene)-2(5H)-furanone; 33is(1′RS,5Z)-3-(1′-Bromohexyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone;and 34 is(1′RS)-3-(1′-Bromohexyl)-5-(dibromomethylidene)-2(5H)-furanone. Thesewere blended into five polymer types. The antifouling efficacy of thesepolymers was compared against control polymers that did not containfuranones.

Polymers were immersed for field testing in Tasmania, Australia. Testingwas conducted at a salmon farm, with panels immersed at 2.0 m depth. Foreach polymer type there were 3 replicate panels for monitoring offouling growth (by underwater photography) and 3 replicate panels forrelease rate analysis. Panels were attached to a 6 m by 2.5 m frame, andeach panel was located in a randomly-chosen position. Samples were takenafter 2, 4, 7, 10, 13, and 16 weeks to assess release rates and fouling.

TABLE 6 Polymers extruded for field trials with synthetic furanonesNumber Polymer 1 Dupont Elvax 470 (ethylene-vinyl acetate. EVA) blank* 2Kemcor HDPE 6095 (high-density polyethylene) blank* 3 Shell PP(polypropylene) blank* 4 Dupont Elvax 470 (EVA) incorporating 5%furanones 26/27 5 Dupont Elvax 470 (EVA) incorporating 5% furanones33/34 6 Kemcor HDPE 6095 incorporating 10% EVA that contained 5%furanones 26/27 7 Kemcor HDPE 6095 incorporating 30% EVA that contained5% furanones 33/34 8 Shell PP incorporating 10% EVA that contained 5%furanones 26/27 9 Shell PP incorporating 10% EVA that contained 5%furanones 33/34 *blank = no furanones added

RESULTS

Control or “blank” polymers (those without furanones) and many of thepolymers incorporating furanones were rapidly fouled. After 28 daysimmersion 100% of the surface area was fouled on most polymers (Table7). Two of the polymers incorporating furanones, however, were highlyinhibitory and had little or no fouling after 28 days (Table 7).

The most efficacious polymer was EVA incorporating furanones 26/27. Onthis polymer type, only 5% of the surface area was fouled after 91 days.Efficacy was reduced at 112 days, but fouling was still stronglyinhibited. This result is better than previous field trials withfuranones, in which analogues of naturally-occurring furanones(extracted from algae) were inhibitive for up to 90 days.

TABLE 7 Antifouling performance of polymers incorporating syntheticfuranones Percentage of surface area covered by fouling 14 28 49 91 112Polymer Type days days days days days Blank polymers* 5 100 100 100 100EVA + 5% furanones 26/27 0 0 5 5 40 EVA + 5% furanones 33/34 0 5 5 25 70HDPE + 10% EVA with 5% 5 100 100 100 100 furanones 26/27 HDPE + 30% EVAwith 5% 5 100 100 100 100 furanones 33/34 PP + 10% EVA with 5% furanones5 100 100 100 100 26/27 PP + 10% EVA with 5% furanones 5 100 100 100 10033/34 *All blank polymers had the same antifouling efficacy

REFERENCES

de Nys R, Wright A D. Konig G M. Sticher O (1993) New halogenatedfuranones from the marine red alga Delisea pulchra (cf. fimbriata).Tetrahedron 49: 11213-11220.

de Nys R. Steinberg P D. Willemsen P, Dworjanyn S A, Gabelish C L, KingR J (1995) Broad spectrum effects of secondary metabolites from the redalga Delisea pulchra in antifouling assays. Biofouling 8: 259-271.

de Nys R, Leya T. Maximilien R, Afsar A, Nair P S R, Steinberg P D(1996) The need for standardised broad scale bioassay testing: a casestudy using the red alga Laurencia rigida. Biofouling 10(1-3): 213-224.

Hodson S L. Burke C (1994) Microfouling of salmon-cage netting: apreliminary investigation. Biofouling 8: 93-105.

Dahl B, Blanck H (1996) Toxic effects of the antifouling agent Irgarol1051 on periphyton communities in coastal water microcosms. Mar PollutBull 32: 342-350.

Takahashi K, Mabuchi K (1997) Leaching mechanism of isothiazolone fromantifouling paints containing Sea-Nine and clathrate Sea-Nine. U.S.Pacific Rim Workshop on Emerging Nonmetallic Materials for the MarineEnvironment.

Vasishtha N, Sundberg D C, Rittschof D (1995) Evaluation of releaserates and control of biofouling using monolithic coatings containing anisothiazolone. Biofouling 9: 1-16.

What is claimed is:
 1. A polymer composition having broad-spectrumantifouling activity comprising a polymer selected from the groupconsisting of ethylene-vinyl acetate copolymer (EVA), high-densitypolyethylene (HDPE), sodium ionomer, copolymer of ethylene and acrylicacid, and mixtures thereof and one or more organic antifouling agentsselected from the group consisting of antifouling agents belonging tothe families of isothiazolones, furanones, and combinations thereof,wherein in use the polymer has broad-spectrum antifouling activity for aprolonged period of at least 100 days when the composition issubstantially immersed in a natural aqueous environment.
 2. Thecomposition according to claim 1 including at least one of the polymersEVA, HDPE, or mixtures thereof.
 3. The composition according to claim 1wherein the isothiazolone antifouling agent is4,5-dichloro-2-n-octyl-4-isothiazolin-3-one.
 4. The compositionaccording to claim 1 wherein the furanone antifouling agent is selectedfrom a mixture of(1′RS,5E)-3-(1′-Bromoethyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanoneand (1′RS)-3-(1′-Bromoethyl)-5-(dibromomethylidene)-2(5H)-furanone; or(1′RS,5Z)-3-(1′-Bromohexyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanoneand (1′RS)-3-(1′-Bromohexyl)-5-(bromomethylidene)-2(5H)-furanone.
 5. Thecomposition according to claim 1 wherein the antifouling agent is usedat a concentration of 0.1 to 20% (w/w) of polymer.
 6. The compositionaccording to claim 5 wherein the antifouling agent is used at aconcentration of 1 to 10% (w/w) of polymer.
 7. The composition accordingto claim 1 wherein the antifouling activity lasts for at least a 200days.
 8. The composition according to claim 7 wherein the antifoulingactivity lasts for at least 250 days.
 9. The composition according toclaim 8 wherein the antifouling activity lasts for at least 300 days.10. The composition according to claim 1 wherein the broad-spectrumantifouling activity in the natural aqueous environment is achieved by arelease-rate about 3-5 μg/cm²/day or less of the antifouling agent overa period of at least 100 days.
 11. The composition according to claim 10wherein the period of release is at least 200 days.
 12. The compositionaccording to claim 11 wherein the period of release is at least 300days.
 13. The composition according to claim 1 wherein the compositionis extruded or molded into fibers or solid structures in the form ofcages, crates or structural materials adapted for use in aqueousenvironments.
 14. An extruded or molded article comprising a compositionaccording to claim 1 wherein the article has sustained broad-spectrumantifouling activity for at least 100 days when substantially immersedin a natural aqueous environment.
 15. A method of preventing orminimizing fouling of a natural aqueous environment for a period of atleast 100 days, comprising immersing a composition of claim 1 in anatural aqueous environment in an amount effective to provide sustainedbroad-spectrum anti-fouling activity for a period of at least 100 days.16. The method of claim 15 wherein the fouling is caused bymicroorganisms or macroorganisms.
 17. A method of preventing orminimizing fouling of a natural aqueous environment for a period of atleast 100 days, comprising immersing an extruded or molded article ofclaim 14 in a natural aqueous environment.
 18. The method of claim 17wherein the extruded or molded article comprises fibers or solidstructures in the form of cages, crates or structural materials adaptedfor use in aqueous environments.
 19. The method of claim 17 wherein thefouling is caused by microorganisms or macroorganisms.
 20. The articleaccording to claim 14, wherein said article is, or forms a part of, anaquaculture apparatus.
 21. The article according to claim 20, whereinthe aquaculture apparatus is used in a shellfish culture.
 22. Thearticle according to claim 20, wherein the natural aqueous environmentis a marine environment.
 23. The article according to claim 20, whereinthe natural aqueous environment is a fresh water environment.
 24. Thearticle according to claim 14, wherein said article is, or forms a partof, plumbing equipment capable of use in a natural aqueous environment.25. The article according to claim 24, wherein said plumbing equipmentis a pipe.